This invention relates to the production of cellulose ether compounds. More particularly, this invention relates to a method for controlling the reaction of cellulose with an etherifying agent.
In known processes for producing cellulose ether compounds, finely divided cellulose is usually reacted with an alkali hydroxide to form alkali cellulose, which in turn is then reacted with an alkyl halide and alkylene oxide in closed, batch reactors. These reactors normally include means for vigorous agitation, and means for heating and cooling to control the reaction temperature. Reaction control of these processes, as well as product quality, is often found to be unpredictable since the rate of reaction is determined by preset temperature/time schedules depending on the limitations of the reactors. Moreover, picking the best temperature/time schedules is extremely difficult since there are many variables which influence the cellulose etherification reaction rate such as heat transfer within the reactor, heat of reaction, amount of byproduct formation, concentration of caustic soda used to make the alkali cellulose, reactivity of the cellulose, and quantity and type of etherifying agents.
Problems concerning process control and product quality can be substantially solved by conducting the reaction at such a slow rate that the rate of temperature change in the reactor would be readily controllable. However, under present and foreseeable conditions, such an approach is impractical and uneconomical. Accordingly, the present practice is to complete the reaction as rapidly as possible, while trying to maintain the best requirements of quality control for the final product. However, since the reaction rate is influenced by so many variables, the temperature profile may vary substantially from batch to batch, as may the uniformity of the products produced.